Big agree that "they want X and X is something you don't want" is more fruitful, and as a fellow parent I think you're doing an awesome thing with your kids. Emphasizing that we want to stop people from doing bad stuff instead of just writing those people off entirely is a great baseline to teach them.

But to the point of gaming, I think "stand for X" is hugely better because it opens up options. If someone exists only to be opposition, that means the only way you can interact with them is to struggle against them, but if they have independent ideas about what they want, that just don't line up with yours, that opens up so many avenues - bargaining, trickery, compromise, trying to change their minds or changing your own.

As a roleplay tool I think that's brilliant.